1. The center gore should always lie flat against your chest.

If the gore is not flat against your chest, then the cup is not large enough to hold all your breast tissue. As a result, tissue is getting smushed into the band, which causes the gore to be pushed away from your chest.

There are a few, rare exceptions, such as pectus excavatum, breasts that are extremely close together (no room for the gore to fit between them), some soft cup nursing bras, and sports bras.

However, for the most part, having the gore sit directly on your chest is one of the most important indication of good fit.

2. Bras are not supposed to hurt.

In fact, they should be the most comfortable thing you wear. You wouldn't wear shoes 100 hours a week that pinched and rubbed, so why put up with that in a bra?

3. You do not have back fat.

So-called back fat and armpit fat are most likely migrated breast tissue. This tissue has been smushed around due to wearing an improperly sized bra. If the bra is too small, the tissue has no where to go, so it escapes out the sides and back.

Make sure you scoop and swoop all this tissue into the cups in order to determine if your bra is fitting correctly.

4. Band size is indicative of your underbust measurement.

Yes, that number does actually mean something. It's not arbitrary like dress sizes (2, 4, 6, 8, etc). If your underbust measurement is an even number, then it will correspond exactly to a band size (32" = 32 band, 38" = 38 band). If your underbust is an odd number, you may need to try both the larger and smaller band to find your preference (29" = either 28 or 30 band, 33" = 32 or 34 band).

5. Cup size is not bra size.

A bra size consists of the combination of band size and cup size. 28D, 38D, and 48D are all different sizes, even though they use the same letter.

Cup size is simply the difference between your bust and underbust. And yes, there are more letters than just A, B, C, D, and DD.